Modeling of deep fracture zone opening and transient ground surface uplift at KB-502 CO2 injection well, In Salah, Algeria

Abstract

The Krechba gas field at In Salah (Algeria), the site of the first industrial scale on-shore CO2 storage demonstration project, is also known for satellite-based ground-deformation monitoring data of remarkable quality. In this work, we focus on the In Salah injection well KB-502, where a double-lobe uplift pattern has been observed in the ground-deformation data. On the basis of previous numerical results, semi-analytical inverse deformation solutions, and seismic analyses, we explain this pattern of uplift as resulting from injection-induced deformation in a deep vertical fracture zone. In this study, we simulate a fracture zone characterized by high permeability and low mechanical stiffness, which activates after a few months of injection, causing irreversible changes in permeability. We study the transient evolution of uplift using the observed injection rate and compare it to the field Interferometric Synthetic Aperture Radar (InSAR) data using the displacement in the satellite line-of-sight. We also carry out a sensitivity study, analyzing the extent of the fracture zone, particularly its height from the reservoir depth. Our analysis supports the notion that the fracture zone is confined within the caprock and does not penetrate into the overlying aquifer.